Causes of Audible Bruit Behind the Ear
The most common cause of an audible bruit behind the ear is vascular pathology, particularly arterial abnormalities such as atherosclerotic carotid artery disease, which creates turbulent blood flow that can be heard as a pulsatile sound. 1
Vascular Causes of Pulsatile Tinnitus
Arterial Causes
- Atherosclerotic carotid artery disease - creates turbulent blood flow that can be heard as a bruit, especially in patients over 50 years with cardiovascular risk factors 1
- Arterial dissection - disruption in arterial wall causing abnormal blood flow 2
- Aberrant internal carotid artery - vascular anomaly where the ICA takes an abnormal course through the middle ear 3
- Fibromuscular dysplasia of the carotids 2
Arteriovenous Causes
- Dural arteriovenous fistulas (dAVF) - abnormal connections between arteries and veins 2
- Arteriovenous malformations (AVM) 2
- Carotid cavernous sinus fistulas 2
Venous Causes
- Transverse sinus stenosis - often associated with idiopathic intracranial hypertension 2
- Sigmoid sinus diverticulum 2
- Persistent petrosquamosal sinus 2
- Prominent mastoid or condylar emissary veins 2
Vascular Tumors
- Paragangliomas (glomus tumors) - highly vascular tumors that can occur in the middle ear (glomus tympanicum) or jugular foramen (glomus jugulare) 2
- Vascular middle ear tumors 2
Bony Abnormalities Causing Pulsatile Tinnitus
- Superior semicircular canal dehiscence - abnormal opening in the bone overlying the superior semicircular canal 2
- Sigmoid sinus wall dehiscence 2
- High jugular bulb - abnormally high position of the jugular bulb 2
- Paget disease - bone disorder that can affect temporal bone 2
Clinical Approach to Evaluating Bruit Behind the Ear
Initial Assessment
- Determine if the tinnitus is pulsatile (synchronous with heartbeat) or non-pulsatile 2
- Check if the sound is objective (examiner can hear it) or subjective (only patient can hear it) 2
- Perform otoscopic examination to identify any vascular retrotympanic mass 2
Imaging Recommendations
For pulsatile tinnitus without visible retrotympanic lesion:
- CT angiography (CTA) of the head and neck is recommended as a first-line imaging modality 2
- Dedicated temporal bone CT can identify bony abnormalities and vascular variants 2
- MRI and MR angiography (MRA) are comparable to catheter angiography in detecting vascular abnormalities 2
- Carotid duplex or Doppler ultrasound is helpful when carotid stenosis is suspected 2, 1
For pulsatile tinnitus with visible retrotympanic lesion:
- High-resolution temporal bone CT without IV contrast is recommended as first-line imaging 2
Common Pitfalls
- Failing to distinguish between pulsatile and non-pulsatile tinnitus, which have different etiologies 2
- Missing objective tinnitus, which should prompt immediate evaluation for vascular abnormalities 2
- Performing biopsy of a retrotympanic mass without ruling out vascular lesion first, which can lead to massive bleeding 3
- Attributing vascular loops in contact with cranial nerve VIII as the cause of tinnitus without searching for other explanations, as these can be normal variants 2
Special Considerations
- In patients over 50 years with pulsatile tinnitus, atherosclerotic carotid artery disease should be highly suspected, especially with associated cardiovascular risk factors 1
- Pulsatile tinnitus can be the first manifestation of carotid artery disease before other symptoms develop 1
- Consultation with a vascular surgeon may be essential in selected cases 1